Cap for an NMR sample tube with inner sealing lip

ABSTRACT

A cap ( 1; 51 ) for an NMR sample tube ( 52 ) having an inner bore ( 3 ) for receiving an open end ( 54 ) of an NMR sample tube ( 52 ), wherein the inner bore ( 3 ) has a narrowing for sealing a received NMR sample tube ( 52 ) against the cap ( 1; 51 ) along the outer periphery of the NMR sample tube ( 52 ), is characterized in that the narrowing is designed as an inner sealing lip ( 4 ). The cap provides good sealing between the cap and the NMR tube, and the cap can be produced from a plurality of materials, in particular, materials with good chemical resistance to NMR solvents.

This application claims Paris Convention priority of DE 10 2007 004 227.4 filed Jan. 27, 2007 the complete disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention concerns a cap for an NMR sample tube, with an inner bore for receiving an open end of an NMR sample tube, wherein the inner bore has a narrowing for sealing an NMR sample tube, received by the cap, along the outer periphery of the NMR sample tube.

A cap of this type is disclosed in DE 103 43 405 A1.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful method for analyzing the structure of chemical compounds. Samples to be investigated are exposed to electromagnetic pulses in a strong, static magnetic field. The electromagnetic response of the sample is measured.

In some measuring methods, the samples are filled into sample tubes, wherein the sample comprises the actual measuring substance and a solvent (NMR solvent). The sample tubes are generally round glass or plastic tubes which are open on one end and have an outer diameter of 3 to 5 mm. Handling, in particular filling, of the sample tubes can be facilitated by using caps which comprise e.g. a funnel-shaped access channel. A cap (closing cap) is usually disposed onto a sample tube during the NMR measurement in order to prevent leakage of the sample, in particular, when the sample is quickly rotated during the NMR measurement.

The sample tubes are conventionally closed by a pin-like plug which is inserted into the sample tube. The plug introduces tensile forces into the wall of the sample tube, which could easily damage the sample tube, in particular, when the sample tube is made from glass.

The cap for an NMR sample tube, which is disclosed in DE 103 43 405, is pushed over the open end of a sample tube. The cap, which is produced from plastic material, has a press fit on an inner bore in which the NMR sample tube is disposed. The press fit comprises a contact surface which has the shape of a circular cylindrical surface and has a slightly smaller inner diameter than the outer diameter of the NMR sample tube in the relaxed state. The press fit typically has an axial extension of a few millimeters. When the sample tube is held, the cap is elastically stretched on the press fit and the entire contact surface abuts the outer periphery of the sample tube, thereby sealing the sample tube with respect to the cap in a gas-tight and liquid-tight fashion.

This conventional method is disadvantageous in that the contact surface and the outer wall of the sample tube must be produced with very close tolerances and must be matched to each other in order to achieve good sealing. Since the press fit abuts the sample tube over a large surface, the force acting on the sample tube can be relatively large, so that it can easily break.

One possibility to reduce the force input into the sample tube and increase the production tolerances consists in using a cap material that has a relatively soft elasticity, such as polypropylene. However, soft cap materials are generally less resistant to many NMR solvents, which limits the range of application.

It is therefore the underlying purpose of the present invention to provide a cap for an NMR sample tube, which provides good sealing between the cap and the NMR sample tube and which can be produced from a plurality of materials, in particular, materials having good chemical resistance to NMR solvents.

SUMMARY OF THE INVENTION

This object is achieved by a cap of the above-mentioned type which is characterized in that the narrowing is formed as an interior sealing lip.

The inner contour of the inventive cap is designed, such that at least one sealing lip forms one defined narrowing which can tightly surround an inserted sample tube, and which fixes the cap on the outer periphery of the sample tube with sufficient pressure. The sealing lip ensures that the cap and the sample tube are sealed with respect to each other in a liquid-tight and gas-tight fashion.

The sealing lip limits the sealing pressure on a defined zone in the cap material (usually plastic material), wherein the zone is much smaller than in prior art. The overall force acting on the sample tube is reduced. This facilitates sufficient elasticity even when materials having a relatively hard elasticity are used, e.g. to compensate for production tolerances when limited forces act on the sample tube. The mechanical load on the sample tube, which is generally made from glass, as well as the danger of breakage are reduced.

Due to the invention, the cap material is no longer restricted to relatively soft plastic materials. Relatively hard plastic materials, in particular, those having good chemical resistance to NMR solvents, can also be used as cap materials.

The inventive sealing lip is typically designed such that its cross-section tapers towards the interior of the inner bore (i.e. radially to the inside). The contact area between the cap and the sample tube is thereby reduced in a simple fashion. The sealing lip is designed such that, when a sample tube is clamped, the sealing lip (or the cap in the area and in the surroundings of the sealing lip) is deformed within an elastic range. In the clamped state, the sealing lip typically abuts the NMR sample tube in an axial direction over 0.5 mm or less, preferably 0.3 mm or less.

In one particularly preferred embodiment of the inventive cap, the sealing lip has a rounded cross-section on the side facing radially inwardly in the relaxed state. The rounded cross-section facilitates insertion of the NMR sample tube, produces little wear, and provides a small contact surface (in particular with small extension in the axial direction) between the cap and the sample tube.

In an alternative preferred embodiment, the sealing lip has a tapering cross-section on the side facing radially inwardly in the relaxed state. This also produces a small contact surface (in particular with a small extension in the axial direction) between the cap and the sample tube.

In a further particularly preferred embodiment, the cap has a uniform, constant wall thickness in the relaxed state in the area of the sealing lip and in the surroundings of the sealing lip. This produces a type of wave shape of the cap wall at locations, similar to a bellows. This geometry facilitates elastic deformation of the cap wall in the area of the sealing lip and thereby reduces the force input into a held sample tube. When radial forces act onto the sealing lip towards the outside (spreading of the sealing lip), the material of the sealing lip can easily deviate radially towards the outside, thereby also elastically axially displacing wall material. The force is thus partially deflected in the material. The extension forces are substantially limited to the spatial extension of the sealing lip itself. The above-mentioned geometry also facilitates the production of the cap through injection molding, which requires forced de-molding.

In one particularly preferred embodiment of the inventive cap, the inner bore comprises a contact ring for holding the NMR sample tube on its outer periphery, wherein the contact ring is different from the sealing lip. The contact ring is designed to fix a held sample tube in addition to the sealing lip and secure it against tilting relative to the cap. The contact ring may thereby define single contact elements, which abut at points or sections, or also a circumferential annular contact area with the sample tube.

In one preferred further development of this embodiment, the contact ring is disposed closer to an insertion opening for the NMR sample tube than the sealing lip. The upper area of the inner bore, which is limited by the sealing lip and in which gas is compressed when the sample tube is inserted and when a closing cap is provided, is particularly small in this case, and the counter force during insertion is correspondingly small.

In another further development of the above-mentioned embodiment, the contact ring is formed by several separate segments. Each segment individually abuts the sample tube. A cap of this type is particularly easy to mount.

In an alternative further development, the contact ring is designed as a further sealing lip which is disposed inside. This increases the sealing tightness and yields a clean two-point abutment which has particularly good mechanical stability.

In another preferred embodiment of the inventive cap, the cap has a groove on its outer periphery for engagement of a sample gripper, which advantageously facilitates handling of the cap, in particular, by an automatic sample gripper. The groove is preferably circumferential, which is however, not absolutely necessary. Several grooves may be provided to reduce weight or for engagement on several planes.

In a further development of this embodiment, the groove is designed such that at least three, in particular four, gripping fingers of the sample gripper can engage the groove, such that the gripping fingers can exert pressure on two outer edges of the groove. The sample gripper can, in particular, be designed as a gripping device of an NMR spectrometer as is described in DE 103 43 405 A1. In this case, the cap is particularly well suited for handling by a sample gripper having gripping fingers.

In another preferred embodiment, the inner bore is substantially circular cylindrical, in particular, wherein the cap has a substantially rotationally symmetrical design. NMR sample tubes having a circular cross-section are widely used and have proven to be useful. The rotational symmetry of the cap facilitates orientation of the cap including sample tube for sample management and for loading an NMR spectrometer.

In another preferred embodiment, the cap has an access channel to the inner bore, which opens into the inner bore in an upper area beyond the sealing lip facing away from an insertion opening for the NMR sample tube. A sample can be filled into a held sample tube via the access channel, e.g. using an injection needle.

In another preferred alternative embodiment, the cap completely closes the inner bore in an upper area beyond the sealing lip facing away from an insertion opening for the NMR sample tube. A closing cap of this type is generally required for closing a sample tube during an NMR measurement, in particular, when the sample tube rotates during the measurement, e.g. during magic angle spinning (MAS) measurements.

In one particularly preferred embodiment, the cap is produced from plastic material. Plastic materials are preferred, which have a relatively hard elasticity and a high chemical resistance to common NMR solvents, in particular chloroform. One particularly preferred plastic material type having a relatively hard elasticity is ORGALLOY LE 6000.

The invention also concerns an NMR sample configuration, comprising a cap and an NMR sample tube, onto which the cap can be disposed, characterized in that the cap is designed as described above in accordance with the invention. The sealing lip yields liquid-tight and gas-tight mutual sealing.

Further advantages of the invention can be extracted from the description and the drawings. The features mentioned above and below may be used individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention.

The invention is shown and explained in more detail in the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic inclined view of an inventive cap in accordance with a first embodiment;

FIG. 2 shows a schematic cross-section through the inventive cap of FIG. 1;

FIG. 3 shows a detailed view of the sealing lip of FIG. 2;

FIG. 4 shows a detailed view of a sealing lip similar to FIG. 3 in accordance with a second embodiment of an inventive cap, with tapering sealing lip;

FIG. 5 shows a schematic cross-sectional view through an inventive sample configuration with an inventive cap and a sample tube held therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 show a first embodiment of an inventive cap 1. The cap 1, which is substantially rotationally symmetric, has an insertion opening 2 through which a sample tube (not shown in FIGS. 1, 2) can be inserted into an inner bore 3 of the cap 1.

The inner bore 3 has a narrowing, i.e. a circumferential sealing lip 4. The sealing lip 4 is rounded in its radially innermost area (i.e. the area disposed most closely to the axis of rotation A). The sealing lip 4 thereby tapers in a radially inward direction (in the direction of arrow R).

The inner bore 3 has a further narrowing, i.e. a contact ring 5. The contact ring 5 is formed by several separate segments 6 which project radially inwardly, thereby tapering to the inside, similar to the sealing lip 4.

A sample tube (not shown, see FIG. 5) can be inserted, with its open end first, into the interior 3 through an insertion opening 2. The open end of the sample tube abuts the inner edge 7 of the inner bore 3 in the inserted state. The outer walls of the sample tube then slightly elastically press the sealing lip 4 in a radial outward direction (opposite to the direction of arrow R), such that the sealing lip 4 abuts the entire outer periphery of the sample tube in a secure and, in particular, gas-tight and liquid-tight fashion.

The cap 1 also has an access channel 8 through which the open end of a held sample tube can be accessed and thereby also the interior of the sample tube, e.g. for filling-in the sample. In an alternative fashion, the cap 1 may also be designed as a closing cap which tightly seals an upper area 9 of the inner bore 3 which is disposed beyond the sealing lip 4 facing away from the insertion opening 2. In this case, the access channel 8 is omitted and replaced by the solid material of the cap.

Several circumferential grooves 10, 11, 12 are furthermore formed on the outer contour of the cap 1. The outer grooves 10 and 12 reduce weight, whereas the central groove 11, at the bottom of which the sealing lip 4 is formed, is provided for engagement with gripper fingers (see FIG. 5).

FIG. 3 shows a detailed section of FIG. 2 in the area of the sealing lip 4. The wall thickness D_(L) of the sealing lip 4 in the radial direction is constant over the entire axial extension of the sealing lip 4. The wall thicknesses D_(U) are identical to the constant wall thickness D_(L) of the sealing lip 4 in the direct vicinity 31, 32 of the sealing lip 4, axially above and below the sealing lip 4. The axial extension of the surroundings 31, 32 of the wall thickness D_(U) is similar to or larger than the wall thickness D_(U).

The inner contour of the sealing lip 4 is approximately symmetrical and two flanks 33 thereof extend at an inclination to the axial direction A′ in each case, however, approximately in a straight line. At the narrowest region 34, the inner contour of the sealing lip 4 is rounded.

In an alternative embodiment (shown in FIG. 4), a sealing lip 4 may be provided, which peaks in the narrowest area 41.

FIG. 5 shows a schematic sectional view of an inventive sample configuration 50 comprising an inventive cap 51 (sleeve) and a sample tube 52 (glass capillary sample container) which is held therein. The sample tube 52 contains a liquid sample 53 and was inserted into the inner bore 3 of the cap 51 with its open end 54 first. The cap 51 is designed as a closure cap.

The sample tube 52 is only clamped by a sealing lip 4, wherein the sealing lip 4 is slightly elastically spread. The outer diameter of the sample tube 52 is thereby slightly larger than the smallest inner diameter of the sealing lip 4 in the relaxed state. Typical outer diameters of sample tubes 52 within the scope of the present invention are 1 mm to 5 mm, in particular 3 mm, 4 mm, or 5 mm. The cap 51 or its sealing lip 4 is matched thereto.

Gripping fingers 55 engage a groove 11, extending on the outer periphery of the cap 51, and abut two outer edges 56 of the groove 11, thus providing secure handling, in particular, transport of the sample configuration 50 with an automatic sample gripper to which the gripping fingers 55 belong. 

We claim:
 1. A cap for an NMR sample tube, the cap comprising: means for defining an inner bore to receive an open end of the NMR sample tube; and an inner sealing lip disposed within said bore to define a narrowing for sealing a received NMR sample tube with respect to the cap along an outer periphery of the NMR sample tube.
 2. The cap of claim 1, wherein, in a relaxed state, said sealing lip has a rounded cross-section on a radially inwardly facing side thereof.
 3. The cap of claim 1, wherein, in a relaxed state, said sealing lip has a tapering cross-section on a radially inwardly facing side thereof.
 4. The cap of claim 1, wherein, in a relaxed state, said cap has a uniform, constant wall thickness in an area of said sealing lip and in surroundings of said sealing lip.
 5. The cap of claim 1, wherein said inner bore has a contact ring for holding the NMR sample tube at an outer periphery thereof, wherein said contact ring differs from said sealing lip.
 6. The cap of claim 5, wherein said contact ring is disposed closer to an insertion opening for the NMR sample tube than said sealing lip.
 7. The cap of claim 5, wherein said contact ring is formed by several separate segments.
 8. The cap of claim 5, wherein said contact ring is formed as a further inner sealing lip.
 9. The cap of claim 1, wherein the cap has a groove on an outer periphery thereof for engagement of a sample gripper.
 10. The cap of claim 9, wherein said groove is designed such that at least three gripping fingers of the sample gripper can engage said groove, such that the gripping fingers can exert pressure on two outer edges of said groove.
 11. The cap of claim 1, wherein said inner bore is substantially circular cylindrical or the cap is substantially rotationally symmetrical.
 12. The cap of claim 1, wherein the cap has an access channel to said inner bore, which opens into said inner bore in an upper area beyond said sealing lip facing away from an insertion opening for the NMR sample tube.
 13. The cap of claim 1, wherein the cap completely closes said inner bore in an upper area beyond said sealing lip facing away from an insertion opening for the NMR sample tube.
 14. The cap of claim 1, wherein the cap is produced from plastic material.
 15. An NMR sample configuration comprising a cap and an NMR sample tube onto which the cap can be disposed, wherein the cap is designed in accordance with claim
 1. 